Another Implementation of Calculator with Several Improvements

This calculator has 3 improvements against the 101_calculator:
1. it can be built successfully by wdk-0.3.18
2. it supports nested parentheses
3. it is left most allied ( 5 - 1 - 1 = (5 - 1) - 1 ) than right ( 5 - 1
- 1 = (5 - (1 - 1) )
The "Reverse Polish Notation" is applied in this program contrasted to
the tree algorithm in 101_calculator